This invention relates to footwear having a shock absorbing system. In particular, a shock absorbing cassette provides improved heel cushioning and stability in a shoe.
Modern athletic shoes combine many elements having specific functions that work together to support and protect the foot. Footwear manufacturers make tennis shoes, basketball shoes, running shoes, baseball shoes, football shoes, weightlifting shoes, and walking shoes for use in those specific sport activities. Each shoe type provides a specific combination of traction, support and protection for the foot to enhance performance.
FIG. 4 is a representation of the skeletal framework 50 of the human foot, which provides the requisite strength to support the weight of the body during many activities. The foot consists of 26 interconnected bones, categorized into three main groups: the phalanges 52 (the distal group), the metatarsus 62 (the middle group), and the tarsus 72 (the posterior group). Although many of the joints between these bones are attached by ligaments and are thus relatively inflexible, there are a number of movable joints that are important to foot flexibility and stability.
The leg bones (the tibia and fibula, not shown) are movably connected to the talus 77 of the foot to form the ankle joint. The hinge-type joint formed by these bones allows both dorsi flexion (upward movement) and plantar flexion (downward movement) of the foot. The talus 77 overlies and is movably interconnected to the calcaneus 78 (heel bone) to form the subtalar joint, which enables the foot to move in a generally rotative, side-to-side motion. The outward and inward motion of the foot during walking or running is associated with this movement about the subtalar joint.
The metatarsus 62 is comprised of metatarsals 63-67 which are relatively long bones that extend forwardly across the middle part of the foot, articulating the tarsus 72 and phalanges 52. Each of the metatarsals are aligned with and articulate to one of the phalanges. For example, the first metatarsal 63 has a metatarsal head 63a which articulates to the hallux (or big toe) at the proximal phalange of the hallux 53a, and the fifth metatarsal 67 has a metatarsal head 67a which articulates to the proximal phalanx 57a of the fifth or smallest digit. The first, second and third metatarsals 63-65 are attached at their proximal ends to the outer, middle and inner cuneiforms 73-75, respectively. The proximal ends of the fourth and fifth metatarsals 66,67 articulate to the cuboid 76.
The phalanges 52 comprise fourteen bones 53a-57c which are associated with the toes, and are hingedly attached to the metatarsals 63-67 for significant movement. The hallux 53 or big toe is the prominent toe for supporting weight, providing propulsive force and for stabilizing the foot. The movements of these bones in the foot play an integral role in controlling pronation and supination of the foot.
A shoe is divided into two general parts, an upper and a sole. The upper is designed to comfortably enclose the foot, while the sole provides traction, protection and a durable wear surface. It is desirable to provide the sole with enhanced protection and cushioning for the foot and leg. Accordingly, the sole of a running shoe typically includes several layers, including a resilient shock absorbing or cushioning layer as a midsole and a ground contacting outer sole or outsole which provides both durability and traction. The sole also provides a broad, stable base to support the foot during ground contact.
Different materials in different configurations have been used in the midsole to improve cushioning and to provide effective foot control. Some shoes use materials of different hardness to provide cushioning and foot control. However, many shoes use only ethyl vinyl acetate (EVA) for cushioning. The cells of this foam tends to break down during use, virtually eliminating the usefulness of the midsole over time.
Although many different types of shoes have been designed for specific sports activities, there apparently has never been a shoe designed for the sport of skateboarding. A skateboarding shoe should have a thin midsole so that a skateboarder can "feel" the board during riding, and when using various footwork positions to perform stunts, in order to maintain better control of the movements of the skateboard. In addition, the shoe must provide adequate cushioning to prevent heel bruising when a skateboarder performs a jump maneuver and lands on the skateboard, the pavement or on some other hard surface.